Why do trucks have so many transmission gears?
In: 354
Semi tractors produce a great amount of torque but do so in a very narrow rpm range, from 1200 to 1500 rpm. In order to get a heavy load moving you need very close ratio gears to be able to keep accelerating and not lose momentum between gears.
When bobtailing ( driving without a trailer ) the load on the motor is low enough that you can skip shift ( skip gears, start in second then shift to 4 then to 6th etc ). When you do that you bog the motor somewhat ( start the gear below 1200 rpm where there is much less torque) but the load is light enough to accommodate. If you try that with a load you won’t have enough power to keep accelerating at such a low rpm and you’d need to shift to a lower gear to accelerate again. The heavier the loads, the more gears you need.
Latest Answers